Flexible pipe and a method for providing buoyancy to a jumper or riser assembly

ABSTRACT

A riser or jumper assembly for transporting production, exportation or injection fluids is disclosed as is a method for providing buoyancy to such an assembly. The riser or jumper assembly includes a first segment of flexible pipe comprising a portion of flexible pipe body and a first and second end fitting, a further segment of flexible pipe comprising a portion of flexible pipe body and a first and second end fitting and an intermediate segment of flexible pipe comprising a portion of flexible pipe body and a first and second end fitting and at least one buoyancy element.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. patent application Ser. No. 13/122,949,filed Apr. 6, 2011, which is the U.S. National Stage of InternationalApplication No. PCT/GB2009/051023, filed Aug. 14, 2009, which in turnclaims the benefit of Great Britain Application No. GB0818500.1, filedOct. 9, 2008.

FIELD

The present invention relates to flexible pipes which may be used toconvey fluids such as production fluids, exportation fluids or injectionfluids from a source to a further location. In particular, but notexclusively, the present invention relates to a riser or jumper assemblyincorporating an intermediate segment of flexible pipe which is used tocarry one or more buoyancy elements.

BACKGROUND

Traditionally flexible pipe is utilised to transport production fluids,exportation fluids or injection fluids such as oil and/or gas and/orwater from one location to another. Flexible pipe is particularly usefulin connecting a sub-sea location to a further sub-sea location or a sealevel location. Flexible pipe is generally formed as a length offlexible pipe body and one or more end fittings at the ends of the pipebody. The pipe body is typically formed as a composite structure oftubular layers of material that form a fluid and pressure containingconduit. The pipe structure is flexible and allows relatively largedeflections without causing bending stresses that impair the pipe'sfunctionality over a desired lifetime. The pipe body is generally, butnot necessarily, built up as a composite structure including metallicand polymer layers. Flexible pipe may be utilised as a flow line overland and/or at a sub-sea location. Flexible pipe may also be used as ajumper or riser.

A riser is an assembly of one or more segments of flexible pipeconnecting a sub-sea source location to a surface station or vessel. Ajumper is an assembly of flexible pipe connecting a sub-sea location toa further sub-sea location. In both instances buoyancy elements haveconventionally been used at desired locations so that in use the riseror jumper assembly adopts a predetermined shape. Conventional buoyancyelements are formed as separate modules manufactured from highly buoyantmaterial or as hollow shells which can be filled with such buoyantmaterial. Such buoyancy modules are conventionally clamped or otherwisesecured to desired positions of the flexible pipe.

From time to time it is known that due to a clamping failure buoyancymodules will move from a desired location on the flexible pipe to anon-desired location. In some instances this can lead to failure of theflexible pipe as over-bending can occur.

A still further problem associated with such buoyancy modules is thatshould the material or integrity of the buoyancy module fail, leading toa lack of buoyancy, a large length of flexible pipe must be recoveredand replaced to overcome the failure.

SUMMARY

It is an aim of the present invention to at least partly mitigate theabove-mentioned problems.

It is an aim of certain embodiments of the present invention to providea riser or jumper assembly or method for manufacturing a riser or jumperassembly in which a location of buoyancy modules is constrained even ifa securing mechanism used to secure the buoyancy module to a flexiblepipe body fails.

It is an aim of certain embodiments of the present invention to providea riser or jumper assembly or method for manufacturing a riser or jumperassembly in which, should a buoyancy module fail, is relatively easy toreplace the module or portion of flexible pipe carrying the module so asto minimise downtime.

According to a first aspect of the present invention there is provided ariser or jumper assembly for transporting production, exportation orinjection fluids from a source location to a target location,comprising:

-   -   a first segment of flexible pipe comprising a portion of        flexible pipe body and a first and second end fitting;    -   a further segment of flexible pipe comprising a portion of        flexible pipe body and a first and second end fitting; and    -   an intermediate segment of flexible pipe comprising a portion of        flexible pipe body and a first and second end fitting and at        least one buoyancy element.

According to a second aspect of the present invention there is provideda method for providing buoyancy to a jumper or riser assembly,comprising the steps of:

-   -   providing lift to at least one portion of flexible pipe via at        least one buoyancy element located between first and second end        fittings of an intermediate segment of flexible pipe comprising        said first and second end fittings and a portion of flexible        pipe body.

Certain embodiments of the present invention provide a riser or jumperassembly which includes an intermediate segment of flexible pipeterminated with a first and second end fitting. One or more buoyancyelements are securable or are secured to the intermediate segment.Should one or more of the buoyancy elements fail the entire intermediatesegment can be replaced in a relatively straightforward manner. Sparesegments can be manufactured at the same time that the flexible pipe orflexible pipes making up the riser or jumper are manufactured tofacilitate the ease of replacement.

Certain embodiments of the present invention provide a riser or jumperassembly in which an intermediate segment of flexible pipe is usedhaving a first and second end fitting. Any movement of a buoyancyelement secured to the intermediate segment, for example due to afailure of a clamping element, results only in motion of the buoyancyelement within the end constraints provided by the first and second endfittings. In this way movement of buoyancy elements along the riser orjumper is at least limited or can be wholly eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described hereinafter,by way of example only, with reference to the accompanying drawings inwhich:

FIG. 1 illustrates flexible pipe body;

FIG. 2 illustrates a jumper and riser;

FIG. 3 illustrates an alternative riser configuration;

FIG. 4 illustrates a riser or jumper assembly;

FIG. 5 illustrates buoyancy modules secured to flexible pipe body; and

FIG. 6 illustrates replacement of an intermediate segment of flexiblepipe.

In the drawings like reference numerals refer to like parts.

DETAILED DESCRIPTION

Throughout this specification reference will be made to a flexible pipe.It will be understood that a flexible pipe is an assembly of a portionof pipe body and one or more end fittings in each of which an end of thepipe body is terminated. FIG. 1 illustrates how a pipe body 10 is formedin accordance with an embodiment of the present invention from acomposite of layered materials that form a pressure-containing conduit.Although a number of particular layers are illustrated in FIG. 1, it isto be understood that the present invention is broadly applicable tocomposite pipe body structures including two or more layers. It is to befurther noted that the layer thicknesses are shown for illustrativepurposes only.

As illustrated in FIG. 1, pipe body includes an innermost carcass layer11. The carcass provides an interlocked metallic construction that canbe used as the innermost layer to prevent, totally or partially,collapse of an internal pressure sheath 12 due to pipe decompression,external pressure, tensile armour pressure and mechanical crushingloads. It will be appreciated that embodiments of the present inventionare applicable to ‘smooth bore’ as well as such ‘rough bore’applications.

The internal pressure sheath 12 acts as a fluid retaining layer andtypically comprises a polymer layer that ensures internal-fluidintegrity. It is to be understood that this layer may itself comprise anumber of sub-layers. It will be appreciated that when the optionalcarcass layer is utilised the internal pressure sheath is often referredto as a barrier layer. In operation without such a carcass (so-calledsmooth-bore operation) the internal pressure sheath may be referred toas a liner.

A pressure armour layer 13 is formed over the internal pressure sheathand is a structural layer with a lay angle close to 90° that increasesthe resistance of the flexible pipe to internal and external pressureand mechanical crushing loads. The layer also structurally supports theinternal-pressure sheath and typically consists of an interlockedmetallic construction.

The flexible pipe body may also include one or more layers of tape 14and a first tensile armour layer 15 and second tensile armour layer 16.Each tensile armour layer is a structural layer with a lay angletypically between 20° and 55°. Each layer is used to sustain tensileloads and internal pressure. The tensile armour layers are counter-woundin pairs.

The flexible pipe body also includes an outer sheath 17 which comprisesa polymer layer used to protect the pipe against penetration of seawaterand other external environments, corrosion, abrasion and mechanicaldamage. One or more layers 18 of insulation may also be included.

Each flexible pipe comprises at least one portion, sometimes referred toas a segment or section of pipe body 10 together with an end fittinglocated at at least one end of the flexible pipe. Usually an end fittingis used at both ends of the segment of flexible pipe body. An endfitting provides a mechanical device which forms the transition betweenthe flexible pipe body and a connector. The different pipe layers asshown, for example, in FIG. 1 are terminated in the end fitting in sucha way as to transfer the load between the flexible pipe and theconnector. Segments of flexible pipe may be joined together in anend-to-end arrangement to make long lengths of flexible pipe. Theadjoined segments may include segments of identical flexible pipe bodyor segments in which the flexible pipe body has different layers and/orphysical properties.

FIG. 2 illustrates a riser assembly suitable for transportingproduction, exportation or injection fluid such as oil and/or gas and/orwater from a sub-sea location 21 to a floating facility. For example, inFIG. 2 the sub-sea location 21 is a connection to a sub-sea flow line23. The flexible flow line comprises a flexible pipe, wholly or in part,resting on the sea floor or buried below the sea floor. The floatingfacility may for example be provided by a platform and/or buoy or, asillustrated in FIG. 2, a ship. The riser 20 is provided as a flexibleriser, that is to say a flexible pipe connecting the ship to the seafloor installation. Alternatively the flexible pipe can be used as ajumper 24.

FIG. 3 illustrates an alternative riser structure connecting a flow line23 to a surface vessel 22. As illustrated in FIG. 3 the riser has afirst part reaching from the seabed flow line 23 to a central suspendedregion 30. A further part extends upwards from the central region 30 tothe surface vessel. Around the central region 30 buoyancy modules aresecured to the flexible pipe body. The buoyancy of the buoyancy modulesand the location of the buoyancy modules is selected so that in use theriser takes a predesigned shape. One advantage of such a riser is thatas the surface where the vessel 22 floats rises or dips the only thepart of the riser linking the vessel to the central buoyed area flexes.In this way over-bending of the riser can be obviated. It will beappreciated that certain embodiments of the present invention can beused with a wide variety of riser or jumper shapes.

FIG. 4 illustrates a riser assembly able to adopt the configuration ofthe riser illustrated in FIG. 3.

The flow line 23 is terminated at an end with an end fitting 40. Thisend fitting is connected in an end-to-end configuration with a furtherend fitting 41 of a first segment 42 of flexible pipe body. A furtherend of the flexible pipe body 42 of the first segment is terminated witha further respective end fitting 43. A bend stiffener 44 is located atthe end of the segment 42 of flexible pipe body close to the end fitting43. The bend stiffener is tapered so as to offer gradually greater andgreater stiffness to the flexible pipe body towards the end fitting 43.This obviates over-bending as will be appreciated by those skilled inthe art.

The end fitting 43 of the first segment of flexible pipe body isconnected to a further end fitting 45 of an adjacent further segment 46of flexible pipe body 46. A further bend stiffener 47 tapers inwardlytowards the central region of the adjacent segment 46 of flexible pipebody. A remaining end of the flexible pipe body 46 is terminated with afurther end fitting 48 with a respective bend stiffener 49. The endfitting 48 of the adjacent segment is connected to an end fitting 50 ofan intermediate segment 51 of flexible pipe body. The end fitting 50terminates a first end of the intermediate segment 51 of flexible pipebody. A remaining end of the intermediate segment 51 of flexible pipebody is terminated with a further end fitting 52. A first bend stiffener53 is located at an end of the flexible pipe body 51 proximate to arespective end fitting 50. A further bend stiffener 54 is locatedproximate to the end fitting 52 terminating the remaining end of theintermediate segment 51 of flexible pipe body. Four buoyancy modules 55are located in a row at the central region of the intermediate segment51 of flexible pipe body. It is to be appreciated that whilst fourbuoyancy modules are indicated one or more buoyancy modules may beutilised according to certain embodiments of the present invention. Thebuoyancy modules and the method of securing these to the flexible pipebody is described hereinbelow in more detail with reference to FIG. 5.

The end fitting 52 terminating an end of the intermediate segment 51 offlexible pipe body is secured in an end-to-end configuration with afurther end fitting 56 of an adjacent segment 57 of flexible pipe body.A remaining end of this adjacent segment 57 of flexible pipe body isterminated with a further end fitting 58. Bend stiffeners 59, 60 arelocated close to respective end fittings 56, 58.

The end fitting 58 of the adjacent segment 57 of flexible pipe body isconnected in an end-to-end configuration with a still further endfitting 61 of an end segment 62 of flexible pipe body. A remaining endof the end segment 62 of flexible pipe body is terminated with arespective end fitting 63. Respective bend stiffeners 64, 65 are locatedproximate to the corresponding end fittings 61, 63.

It is to be appreciated that one or more segments of flexible pipe arethus provided on either side of an intermediate segment of flexible pipewhere buoyancy modules are located. It will be appreciated that ratherthan the two segments illustrated on either side of the intermediatesegment shown in FIG. 2, one, two or any number of segments may beprovided on either side of the intermediate segment. Likewise, it is notessential that the numbers of segments of flexible pipe body are thesame on either side of the intermediate segment. It is also to beappreciated that one, two or more intermediate segments of flexible pipebody may be utilised according to certain embodiments of the presentinvention.

FIG. 5 illustrates an alternative intermediate segment 100 of flexiblepipe in more detail. The intermediate section of pipe has a first endterminated by an end fitting 150 and a further end terminated by afurther end fitting 152. A length of flexible pipe body 151 isterminated at both ends by a respective one of the end fittings 150,152. As illustrated in FIG. 5 the flexible pipe body has a lengthextending between the two end fittings. A bend stiffener 153 is securedto the first end fitting 150 and a further bend stiffener 154 is securedto the further end fitting 152 at the other end of the segment. Eachbend stiffener is a generally tapered device, as will be appreciated bythose skilled in the art, used to moderate the stiffness of the flexiblepipe from a central region, where flexibility is defined by thecharacteristics of the flexible pipe body, to the rigid end fittings150, 152. Six buoyancy modules 155 ₀₋₅ are located adjacent to eachother in a line between the bend stiffeners. Whilst six buoyancy modulesare illustrated in FIG. 5 it will be appreciated that any number ofbuoyancy modules, including one, two or more, may be utilised dependentupon the configuration and amount of buoyancy required in the riser orjumper in use. The buoyancy modules 155 ₀₋₅ are secured to the flexiblepipe body 151 via a conventional means such as via a clamping mechanism.

The intermediate section 100 has an overall length L equal to thecombined length of the two end fittings E plus the combined length ofthe two bend stiffeners B plus the remaining length Z of flexible pipebody between the inner ends of the bend stiffeners.

An inwardly facing end 160 of the first bend stiffener 153 provides anabutment surface for any buoyancy module which becomes unsecured fromthe flexible pipe body 151. An inwardly facing end 161 of the furtherbend stiffener 154 likewise provides an abutment surface against whichany buoyancy module 155 ₀ will abut should it become detached from theflexible pipe body. Each buoyancy module itself has a first and furtherside wall 162 ₀₋₅, 163 ₀₋₅ against which adjacent buoyancy modules willabut should they become detached from the flexible pipe body.

It will be appreciated that by selecting the lengths of the endstiffeners and the length of flexible pipe body used during a designstage the distance Z between the abutment ends 160, 161 of the bendstiffeners can be precisely set so that there is sufficient distancebetween the buoyancy modules and the ends of the bend stiffeners toallow the flexible pipe to adopt a desired shape during use but with noor little excess room so that should a buoyancy module fail movement ofthose buoyancy modules is constrained completely or to at least acertain extent.

For example, should the mechanism by which the buoyancy module 155 ₅ atthe end of the row is attached to the flexible pipe body 151 fail thebuoyancy module will effectively become free to move along the length ofthe flexible pipe body. However, its motion is constrained by theabutment surface 160 of the inwardly facing end of the bend stiffener153 or by a side wall 162 ₄ of the adjacent buoyancy module 155 ₄.

FIG. 6 illustrates how the intermediate segment 30 of flexible pipeshown in FIG. 4 may be replaced. The intermediate segment 100 shown inFIG. 5 could be replaced in a similar way. It will be appreciated thatsuch replacement may be required or desired when a part or parts of theflexible pipe segment 30 fail or when the characteristics offered by theintermediate segment 30 are no longer optimum according tocharacteristics of the environment where the riser or jumper assemblyare used. In such a situation the old intermediate section 30 _(OLD) isreplaced by a new intermediate section 30 _(NEW). For example should oneor more buoyancy modules 155 become detached from the flexible pipe body51 or should one or more of the buoyancy modules fail, such as by anouter shell being breached and flooding with seawater, the end fitting50 at a first end of the intermediate segment of flexible pipe body canbe detached from the adjoining end fitting 48 of the adjacent segment offlexible pipe. Likewise, the further end fitting 52 of the intermediatesegment of flexible pipe can be detached from the end fitting 56 of thefurther adjacent segment of flexible pipe body. A new intermediatesegment 30 _(NEW) is then brought into position and respective endfittings secured together. The replacement intermediate segment may havea similar or different length to the previously used segment. It ishighly convenient if the intermediate segment of flexible pipe ismanufactured at the same time as the remaining segments of any riser orjumper assembly. One, two or more replacement segments may bemanufactured at this time and then stored for later use if needed.

Certain embodiments of the present invention thus create a flexible pipesystem useable in a wide variety of environments, for example, deep andultra-deep water operations. Effects of buoyancy module clamp failureare thus minimised by confining the buoyancy modules which are requiredbetween two end fittings. These or the bend stiffeners attached to theend fittings act as buoyancy stoppers avoiding modules significantlychanging position. This can be achieved whilst having a low impact onsystem configuration requirements and service life.

Certain embodiments of the present invention allow a relatively fastrecovery of the flexible pipe system in the case of one or more buoyancymodule failures or where a net buoyancy capacity decreases due to modulewater saturation or flexible pipe structure premature failure. Fastrecovery can be achieved by replacing the damaged buoyancy riser orjumper segment by a spare, previously assembled, segment. Thiseliminates the necessity for offshore pipe completion activities andconsiderably reduces a time required to restart pipeline operation.

The jumper or riser assemblies utilise one or more intermediate segmentseach having a total length defined by a required buoyancy length plusthe length required for the flexible pipes ancillary assembly. Thisincludes end fittings and bend stiffeners and other such devices. Theintermediate segment is positioned in the overall jumper or riser systemat a specific location defined during global analysis in order tomaximise the fatigue service life and guarantee that the flexible pipeoperational conditions are respected.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

1. A riser or jumper assembly for transporting production, exportationor injection fluids from a source location to a target location,comprising: a first segment of flexible pipe comprising a portion offlexible pipe body and a first and second end fitting; a further segmentof flexible pipe comprising a portion of flexible pipe body and a firstand second end fitting; and an intermediate segment of flexible pipecomprising a portion of flexible pipe body and a first and second endfitting and at least one buoyancy element.
 2. The riser or jumperassembly as claimed in claim 1, further comprising: the first segment offlexible pipe comprises the first and second end fittings terminatingrespective first and second ends of the portion of flexible pipe body ofthe first segment and a first and second bend stiffener each secured toa respective end fitting of the first segment.
 3. The riser or jumperassembly as claimed in claim 1, further comprising: the further segmentof flexible pipe comprises the first and second end fittings terminatingrespective first and second ends of the portion of flexible pipe body ofthe further segment and a first and second bend stiffener each securedto a respective end fitting of the further segment.
 4. The riser orjumper assembly as claimed in claim 1, further comprising: theintermediate segment comprises first and second end fittings terminatingrespective first and second ends of the portion of flexible pipe body ofthe intermediate segment and a first and second bend stiffener eachsecured to a respective end fitting of the intermediate segment.
 5. Theriser or jumper assembly as claimed in claim 4, further comprising: theat least one buoyancy element is secured at a respective locationbetween the first and second bend stiffeners of the intermediatesegment.
 6. The riser or jumper assembly as claimed in claim 5, furthercomprising: each buoyancy element is clamped to an outer surface of theportion of flexible pipe body of the intermediate section,
 7. The riseror jumper assembly as claimed in claim 1 wherein the length of theintermediate segment is equal to a combined length of two of the endfittings plus a required buoyancy length.
 8. The riser or jumperassembly as claimed in claim 1, further comprising: at least one stillfurther segment of flexible pipe comprising a portion of flexible pipebody and a respective first and second end fitting.
 9. A method forproviding buoyancy to a jumper or riser assembly, comprising the stepsof: providing lift to at least one portion of flexible pipe via at leastone buoyancy element located between first and second end fittings of anintermediate segment of flexible pipe comprising said first and secondend fittings and a portion of flexible pipe body.
 10. The method asclaimed in claim 9, further comprising the steps of: providing lift tothe intermediate segment of flexible pipe between a first and furthersegment of flexible pipe.
 11. The method as claimed in claim 9, furthercomprising the steps of: identifying a failure of a buoyancy element ofthe at least one buoyancy element; and subsequently replacing theintermediate segment with a replacement intermediate segment comprisinga replacement portion of flexible pipe body, replacement first andsecond end fittings and at least one replacement buoyancy element. 12.The method as claimed in claim 11 wherein the step of identifying afailure comprises: identifying when a damp clamping the buoyancy elementto an outer surface of flexible pipe body has failed; or identifyingwhen the buoyancy element has become saturated; or identifying that theriser or jumper assembly is not adopting a predetermined shape.
 13. Themethod as claimed in claim 11 wherein the replacement intermediatesegment comprises a spare, previously assembled, segment of flexiblepipe.